Prostaglandins (PG) have an essential role in regulating ovarian function including key aspects of ovulation, luteinization, and luteal regression. Despite this central role in reproductive physiology the temporal and cellular patterns of expression for the PG receptors, as well as the hormonal regulation of this expression, have not been defined. With the recent cloning of the cDNAs for the various subtypes of PGE and PGF/2alpha receptors, an analysis of both the protein and mRNA for these receptors is possible. We have validated highly sensitive and quantitative assays for the PGF/2alpha receptor mRNA and protein as well as the measuring PGF/2alpha responsiveness. The research proposed in this application is designed to evaluate the mechanisms involved in expression of the PGF/2alpha receptors and responsiveness during luteinization and luteolysis. Our working hypotheses for these studies is that the LH surge, or other aspects of the luteinization process, induce the expression of PGF/2alpha receptors and PG-responsive intracellular pathways, thus, establishing the cellular mechanisms for ovulation, luteinization, and regression of the corpus luteum. The Specific Aims are: 1) Characterize the temporal pattern for the in vivo expression of PGF/2alpha receptors during late follicular and early luteal development. 2) Determine the role of cAMP-dependent protein kinase, progesterone, and de novo protein synthesis in the differentiation of PGF/2alpha responsiveness in cultured follicular cells. 3) Determine whether small luteal cells can be induced by forskolin or hCG to express FP receptors, a property indicative of the large luteal cell phenotype. Determine the intracellular effector systems involved in PGF/2alpha-induced stimulation of mRNA for PGH synthase-2 and inhibition of mRNA for the PGF/2alpha receptor. 4) Determine the response of early and mid-cycle corpora lutea to PGF/2alpha in terms of down regulation of PGF/2alpha receptors, secretion of oxytocin, induction of mRNA for PGHS-2, and inhibition of expression of mRNA for 3beta-Hydroxysteroid Dehydrogenase. These studies will advance our knowledge of physiologic, intracellular, and molecular mechanisms regulating the expression of mRNA, protein, and intracellular response pathways for the PGF/2alpha receptor. This will not only advance our current knowledge of reproductive physiology, but will allow for the rational development of contraceptives or infertility treatments that target prostaglandin action in the ovary.